A physics student is standing on an initially motionless, frictionless turntable with rotational inertia 0.31 kg·m2. He's holding a wheel of rotational inertia 0.22 kg·m2 spining at 125 rpm about a vertical axis. When he turns the wheel upside down, student and turntable begin rotating at 79 rpm.
(a) What is the student's mass, considering him to be a cylinder 30 cm in diameter?
(b) How much work did he do in turning the wheel upside down? Neglect the distance between the axes of the turntable and wheel.
A physics student is standing on an initially motionless, frictionless turntable with rotational inertia?
When the student turns the wheel 180 degrees, the angular momentum of the spinning wheel is transferred to the angular momentum of the platform. student.
L before = L after
L = I w
L(before) = I(wheel)w(wheel) = (0.22)(125rpm)
I(total) = I(student) + I(platform)
= (1/2)MR^2 + 0.31 =(1/2)M(0.075)^2 +0.31
= 0.0028125M + 0.31
L(after) = I(after)w(after)
= ( 0.0028125M + 0.31)(79rpm)
L(before) = L(after)
(0.22)(125rpm) = ( 0.0028125M + 0.31)(79rpm)
0.348101266 = ( 0.0028125M + 0.31)
0.038101266 = 0.0028125M
M =13.5471168 kg seems like a small student to me. You better check my math
b)For pure rotation, the net work is equal to the change in rotational kinetic energy
Work = (1/2) I w(f)^2 - (1/2) I w(i)^2
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